1. Field of the Invention
The present invention relates to a light-emitting unit, and a method for producing the same as well as a lead frame used for the light-emitting unit, and more particularly to an effective technology applied to a surface mount type light-emitting unit wherein a light-emitting device such as light-emitting diode (LED) has been used.
2. Prior Art
Heretofore, a light-emitting unit wherein a light-emitting device such as light-emitting diode is used has been utilized for a variety of pilot lamps, a backlight for display devices and liquid crystal display, an exposure light source for printer head, optical communications and the like extending over a wide range. There are two types of the above-described light-emitting unit, one of which is a through hole mount type unit wherein a first lead (cathode) and a second lead (anode) are inserted into through holes in a mount board, and they are soldered, respectively; and the other of which is a surface mount type unit wherein a first lead and a second lead are soldered with respect to a pad (terminals) provided on a surface of such mount board.
The above-described through hole mount type light-emitting unit is arranged in, for example, such that a first electrode (not shown) of a light-emitting device 1 is bonded to an end of a first lead (cathode) 2 by the use of a conductive adhesive such as a silver paste, a second electrode (not shown) of the light-emitting device 1 is connected to a second lead (anode) 3 with a bonding wire 5, and the light-emitting device 1, a bonding section of the first electrode and the first lead 2 in the light-emitting device 1, and a connecting section of the second electrode and the second lead in the light-emitting device 1 are sealed with a clear insulator 4 as shown in FIG. 1(a).
Furthermore, an extreme end of the first lead 2, in other words, a part to which the light-emitting device 1 has been bonded is provided with a cup-shaped reflection member 11, the bottom of which is flat, as shown in FIGS. 1(a) and 1(b), whereby light output from the light-emitting device 1 is reflected by a surface of the reflection member 11 to elevate convergence of light, so that high-powered light can be obtained.
In the through hole mount type light-emitting unit, the first lead 2 and the second lead 3 are pin-shaped and protrude from the insulator 4 as shown in FIG. 1(a). As a result, a height T from a mount surface becomes high in the case when the light-emitting unit is mounted on a mount board, so that it is difficult to downsize an electronic device in which the above-described light-emitting unit has been used.
Thus, there has been a surface mount type light-emitting unit in which a height from its mount surface can be reduced, whereby it is possible to downsize easily an electronic device wherein the above-described light-emitting unit was used.
As an example of the above-described surface mount type light-emitting unit, there is the one wherein a wiring board 12, which is prepared by forming a cathode electrode pattern 1202 and an anode electrode pattern 1203 on a surface of an insulating substrate 1201, is used, a light-emitting device (light-emitting diode) 1 is bonded onto the cathode electrode pattern 1202, while an anode (not shown) of the light-emitting diode 1 is connected to the anode electrode pattern 1203 of the wiring board 12 by means of a bonding wire 5, and a clear insulator 4 is disposed on the wiring board 12 as shown in FIG. 2(a) (see Japanese Patent Laid-Open No. 242526/1995).
In the wiring board 12, for example, as the one used for a tape carrier package, a conductive pattern composed of the cathode electrode pattern 1202 and the anode electrode pattern 1203 is disposed on a surface of an insulating substrate 1201 such as a polyimide resin substrate, and a glass-reinforced epoxy resin substrate prepared by impregnating a glass cloth, as a base material, with epoxy resin. In this case, the cathode electrode pattern 1202 and the anode electrode pattern 1203 are drawn out via an end surface through hole, respectively, in a backside of a surface on which the light-emitting device (light-emitting diode) is to be bonded.
Moreover, in a light-emitting unit as shown in FIG. 2(a), a reflection member 11 is disposed so as to surround a periphery of the light-emitting diode 1 for the sake of elevating convergent performance of light output from the light-emitting diode 1. In addition, the insulator 4 is provided with, for example, a convex lens section 41, as shown in FIG. 2(a), for controlling convergent performance of light to be output.
Furthermore, there is, for example, another light-emitting unit involving a reflecting cup section 17 for containing the light-emitting device (light-emitting diode) 1 on the top of a sheet metal substrate 13 as shown in FIG. 2(b) as a surface mount type light-emitting unit as described above (see Japanese Patent Laid-Open No. 252524/2000) other than the light-emitting unit wherein a wiring board 12 as shown in FIG. 2(a) has been used.
In the light-emitting unit shown in FIG. 2(b), the sheet metal substrate 13 made of, for example, copper, iron and the like is fabricated by press-molding any material sheet of them into a predetermined shape, and the resulting sheet metal substrate 13 is divided into two section with a slit 16 parallel to stepped portions 14 and 15 formed on sides opposite to each other in the sheet metal substrate 13. Besides, a reinforcing third resin 21 is disposed on a backside of the sheet metal substrate 13.
A method for producing a light-emitting unit as shown in FIG. 2(b) will be described briefly. First, a sheet metal substrate 13 is press-molded to form stepped portions 14 and 15 as well as a reflecting cup section 17, besides a slit 16 parallel to the stepped portions 14 and 15 is defined to divide the sheet metal substrate 13.
Then, the slit 16 is closed by means of, for example, a masking tape 18, and a space defined by the sheet metal substrate 13 in its back side is filled with a third resin 21 such as epoxy resin to reinforce the sheet metal substrate 13.
Next, a light-emitting diode 1 is placed on the reflecting cup section 17, an under surface electrode of the light-emitting diode 1 is fixed to the bottom of the reflecting cup section 17 by means of a conductive adhesive, and an upper electrode of the light-emitting diode 1 is connected to a wire bonding electrode positioned on the stepped portion 14 across the slit 16 by means of a bonding wire 5.
Thereafter, the reflecting cup section 17 is filled with a first resin 19 into which a wavelength converting material has been incorporated, and the whole of the light-emitting unit other than a lens section 41 is sealed with a second resin 20.
However, a through hole mount type light-emitting unit as shown in FIGS. 1(a) and 1(b) in the above-described prior art has involved such a problem that it is difficult to downsize the unit, so that it is also difficult to downsize an electronic device wherein the above-described light-emitting unit has been used.
Furthermore, a surface mount type light-emitting unit wherein a wiring board 12 has been used as shown in FIG. 2(a) has involved such a problem that a light-emitting diode 1 has been bonded onto the wiring board 12, so that heat generated from the light-emitting diode 1 is released to the outside through the wiring board 12. In this connection, however, there may occur such a problem as mentioned below, because a coefficient of thermal conductivity in an insulating substrate 1201 is low. Namely, the heat generated from the light-emitting diode 1 cannot be released sufficiently in the case where the light-emitting diode 1 is high-powered, resulting in high calorific value, or the case where the light-emitting diode 1 is allowed to emit light continuously for a long period of time, and hence the interior of the light-emitting unit becomes easily high-temperature.
When the light-emitting diode 1 retains heat and it becomes high-temperature, there arises such a problem that electrical characteristics of the light-emitting diode 1 change, so that light-emitting efficiency decreases.
Moreover, since a reflection member 11 prepared in a separate process from that of preparing the wiring board 12 has been bonded, there has been such a problem that manufacturing processes and the number of parts to be used increase, so that its manufactures' costs increase also.
Furthermore, it is difficult to make an insulating substrate 1201 thinner to ensure a strength, so that there has been such a problem that it is difficult to make thinner and to downsize the whole of a unit.
Still further, a surface mount type light-emitting unit wherein a sheet metal substrate 13 is used as shown in FIG. 2(b) requires a masking tape 18, a third resin 21 and the like, so that the number of components (materials) to be used for producing the light-emitting unit increases, besides production steps therefor become complicated, and it results in a problem of increasing manufactures' costs for the unit.
Yet further, in the light-emitting unit where in the sheet metal substrate 13 has been used, since the third resin 21 is disposed on a back side with respect to a surface on which the light-emitting diode 1 was bonded, releasing characteristics of heat generated from the light-emitting diode 1 are inferior, so that heat accumulates easily in the unit, resulting in a problem of decreasing light-emitting efficiency.
In addition, since stepped portions 14 and 15 are defined on a sheet metal substrate 13 in a light-emitting unit wherein the sheet metal substrate 13 as described above and shown in FIG. 2(b) has been used, there is such a problem that it is difficult to make the unit thinner and to downsize the same.